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Old 22nd June 2004, 06:48 PM   #1
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Join Date: Jun 2004
Location: Irvine, Ca
Default Quick Relay/Timer Help Needed

I'm a circuit novice building a timing circuit for a drag racing type light tree. I've built several cascaded NE555 chips to get the correct timing. Third figure down in this link
http://home.cogeco.ca/~rpaisley4/LM555.html#20
I've connected the outputs of the timers to relays (and LEDs to shows the output is working). These relays are suppose to drive the light bulbs on the tree.

I'm having trouble with the relays. I don't know much about relays other than how they basiclly work. The normally open relays seem to be sticking closed.

First I used some cheap reed relays, I thought that was the problem. But I replaced one with a better quality SPDT relay (leaving the NC contact unconnected), and it sticks even worse. I'm pretty sure I'm within all the specifications of relay.

I have it set where the output of the 555 chip goes across the coil of the relay and the 'throw' of the relay connects the + side of the 120VAC. - side of the 120VAC is always connected.

Please help. People are expecting me to have this running on Saturday.

Jay W
505/287 Dakota
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Old 23rd June 2004, 12:57 AM   #2
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Location: boston Ma.
You may be finding that the filaments draw a lot of current-- It's in the nature of the beasties that a cold filament is close to a dead short--Its amperage becomes reasonable right away...
Solutions-- A solid state relay- uses 5V at like no Ma. (!)--I can get them cheap on Ebay but you don't have the time.....
@: regular bosch/hella relay- Yuve seen them-- they have a 40 amp rating AND a coil that uses a fair amount of juice (LIke 125 Ma./12V), so they'll have to be cascaded with your reed relays! Use a few.
set 'm up for 120 V even tho they are rated for 14.2---they'll be ok if no
one goes into your light bar and gets shocked. upgrade next week!
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Old 23rd June 2004, 06:34 PM   #3
lgreen is offline lgreen  United States
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Join Date: May 2003
Location: San Diego, USA
Default relays

Relays energize at low voltage, about 5 volts. You may have the type that turns "on" at 5 volts (or 12 or some other voltage) and then stays on until you give it a negative voltage of the same amount. Make sure you give it the right amount of voltage at the right polarity to turn it on and off, look at the data sheet. What model relays are you using?
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Old 24th June 2004, 06:05 PM   #4
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Join Date: Jun 2004
Location: Irvine, Ca
I was using some pretty good relays from radio shack (and I'm sure I was within the specs). But I gave up and found a place close to me that sold ready made relay boards.

http://www.smarthome.com/7278.html

A minor rewire of my circuit board and I output the 12V signals to the ready made relays then from there off to the lights. At 2am last night it was working.

I like this design better anyways. It keeps my control board as just 12VDC (no 120AC to deal with). And these relays are capable of handeling more amperage, so I can go 50 or 100W bulbs if I find the 25Watts don't do the job.

Thanks guys.

Jay W
505/287 Dakota
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